An international team of astrophysicists says the universe is continuing to expand at an accelerating rate, challenging recent claims that cosmic expansion may be slowing down.
The researchers have disputed a study published last year that suggested the universe’s expansion was beginning to decelerate. Their findings support the standard cosmological model, which proposes that dark energy remains the mysterious force driving the accelerating expansion of the universe.
The international team includes two Nobel Prize winners and scientists from leading institutions worldwide. According to the researchers, the controversy sparked by the earlier study resulted from problems in the analysis rather than evidence that the established understanding of the universe had collapsed.
The new research was published in Monthly Notices of the Royal Astronomical Society.
New analysis challenges claims that cosmic expansion is slowing
The study directly responds to research by a South Korean team, which suggested that the universe may have entered a period of slower expansion. That earlier work proposed that dark energy, a force that acts against gravity on cosmic scales, could be weakening over time.
Lead author Dr Phil Wiseman of the University of Southampton said the latest analysis supports the measurements astronomers have used for decades.
“Previous widely accepted measurements were indeed good, and our current understanding of the fate of the universe remains robust,” said lead author Dr Phil Wiseman from the University of Southampton.
“Thankfully, we have avoided this crisis, but the mystery remains as to why the rate of expansion of the universe is still accelerating.
“By proving that our measurements are correct, we can return to trying to understand what dark energy actually is, rather than questioning whether it exists at all.”
Type Ia supernovae revealed the universe’s accelerating expansion
The international research team includes Professors Adam Rees and Brian Schmidt, who shared the 2011 Nobel Prize in Physics with Professor Saul Perlmutter.
Their Nobel Prize-winning work was based on observations of Type Ia supernovae, extremely bright stellar explosions produced by white dwarf stars. By comparing these explosions at different distances, astronomers found that more distant objects appeared to be moving away faster. This evidence led scientists to conclude that the expansion of the universe is accelerating.
That interpretation has remained widely accepted. However, a South Korean study published last year challenged the conclusion, arguing that Type Ia supernovae may not all reach the same peak brightness as the universe ages.
If correct, that finding could mean astronomers had misinterpreted supernova data and incorrectly concluded that cosmic expansion was accelerating when it was actually slowing.
Researchers find problems with the original analysis
A research team led by the University of Southampton said its analysis identified significant problems in the way the ages of exploding stars were estimated. According to the researchers, earlier work treated the age of a galaxy as though it were the same as the age of the individual stars that later exploded as supernovae.
The researchers also said the South Korean study did not sufficiently account for the mass of the galaxy hosting each supernova. Correcting for the mass and environment of the host galaxy is a standard procedure in modern cosmology and helps scientists produce more accurate measurements.
Professor Rees said: “Extraordinary claims require particularly careful examination.”
“What we found is that when we calibrate these supernovae to account for different host environments and stellar populations, the evidence for cosmic acceleration remains remarkably consistent.”
The mystery of dark energy remains unsolved
Professor Mark Sullivan, also of the University of Southampton, said that challenging established theories and observations remains an essential part of the scientific process.
“This is how progress is made. Although this idea turned out to be incorrect, it opened up new ways of thinking about how supernovae work and how to measure dark energy more accurately,” he added.
Co-author Dr Brody Popovich said the debate also allowed researchers to examine the astrophysics of supernova explosions more closely and reassess the assumptions behind cosmological measurements.
“We’ve recently been focusing on the astrophysics of these explosions and how they influence cosmology,” he said.
“This was a valuable opportunity to review all of our assumptions. It turns out that we understand these effects and already account for them in our cosmological measurements.”
Source: www.sciencedaily.com